In the last years inorganic semiconductor (particularly CdSe and CdS) quantum dots (QDs) have received great attention
for their important optical properties. The possibility to tune the emission wavelength, together with their high
fluorescence quantum efficiency and photostability, can be exploited in photonic and optoelectronic technological
applications. The design of DFB devices, based on QDs as active optical material, leads to the realization of compact
laser systems. In this work we explore the use of an inorganic/organic hybrid material composed of CdSe-ZnS
semiconductor quantum dots doped into a zirconia sol-gel matrix for optical gain applications. Through the use of soft
lithography on a sol-gel germania-silica hybrid, large scale distributed feedback gratings can be created. Used in
conjunction with the CdSe-ZnS/ZrO2 hybrids, these gratings can act as microcavities and allow for the realization of true
lasing action. The lasing properties within these devices are characterized in the femtosecond regime by both one- and
two-photon excitation. From experimental data the value of the optical gain of the core-shell quantum dot samples has
been estimated. Moreover, one- and two-photon lasing threshold and stability are reported.
A hybrid organic-inorganic sol-gel material based on 3-(glycidoxypropyl)-trimethoxysilane (GPTMS), an organically modified alkoxide containing an epoxy ring in the organic functional group, and titanium isopropoxide Ti(OPri)4 has been synthesised. The presence of Ti alkoxide is important in order to increase the refractive index and to improve the mechanical and physical properties of the film. A basic catalysis has been used to perform the hydrolysis/condensation reactions of the inorganic network and to preserve the presence of unreacted epoxy rings. The epoxy groups are thus available in the final solid state films for the UV-photopolymerization process. The photopolymerization allows one to increase the refractive index and to pattern the film directly.
The modification of the hybrid sol-gel TiO2 matrix microstructure during the thermal treatment and the interaction with the UV light have been investigated by FT-IR and UV-Vis spectroscopies, DTA and TGA thermal analysis. The sol-gel film thickness and roughness have been analyzed by a profilometer: the films possess high optical quality and well controlled thickness, ranging from 500 nm to 2 μm. The refractive index of sol-gel thin films was measured by m-line spectroscopy and ellipsometry. An increase of the refractive index in the range 0,02÷0,1 was achieved, depending on the UV irradiation dose.